Polar accelerometer



Aug. 20, 1963 POLAR ACCELEROMETER Filed Jan. 25, 1960 2 Sheets-Sheet 1 SCOPE SIDNEY LEES INVENTOR.

{um 41.; w. W gra /Ida ATTORNEYS Aug. 20, 1963 s. LEES POLAR ACCELEROMETER 2 Sheets-Sheet 2 Filed Jan. 25, 1960 FIG. 6

INVENTOR.

SIDNEY LEE 5 ATTORNEYS reed exteii 3,101,003 POLAR ACCELERQMETER Sidney Lees, 544 Walnut St, Newton, Mass. Filedlan. 25, 1960, Ser. No. 4,4?7

' l1 Qlaims. (1. 73-517) {This invention relates to accelerometers and more particularly comprises a new and improved linear accelerometer capable o fimeasuping accelerations in any direction parallel to the plane in which the instrument is oriented. t Q,

In theprior" art devices of which I am aware, linear accelerometers :are unidirectional, that is, they are capable of .nieasuring.acceleration in but one direction deter mined by the orientation of the instrument. in order to measure accelerations in diiterent directions, it has been necessary. to employ twoindependently operated output indicators, each unidirectional, and utilize thetwo indicators to obtain vector components of the acceleration along {the 'x and y coordinates. Thereafter the information obtainedfb'y eachindicator has beenfcombincd to determine the. magnitude and direction of the acceleration.

The primary objectof my invention is to provide a linear accelerometer capable of measuring directly accelerations in any direction and indicate not only the magnitude of the acceleration ,but its direction as well. To accomplish this and other objects, one embodiment of my invention includes a magnetic circuit composed of a cylindrical armature and a surrounding magnetic field piece, The magneticiiezld piece includes an annular pole nited SW38 0 V the coilassumes' a particularangular position, the direction of .the displacement of the armature may be established.

In a second embodiment of my invention the armature isreplaced by a non-conducting cylindrical bobbin having, a metallic cylindrical skin which forms one plate oia capacitor. Thebobbin like the armature is elastically restrained in a referenceposition and displaces in response to acceleration of its support. A pair of electrodes disposed parallel to the axis of the bobbin are spaced from its m etallic skin and form the second plate of the capacitor. The electrodes are displaced 180. apart about the bobbin axis and rotate about a fixed axis coincidentwi-th the axis of the bobbin in its re erence position. A potential is impressed across the condenser plates and the capacitan'ce may be measured by a circuit identical'to that used in theother embodiment of my invention, The capacie tance will of course vary in response to di'spla-cementof the bobbin which ciiects a change of gap width between the plates. The direction of displacement may also be readily determined in the same manner as employed in tbepreferred embodiment of my invention] companying drawing, in which;

piece having a pole face cylindrical shape which surrounds the armature and is spaced a uniform distance from it to definefan annular gap in the circuit of unitbrrn width throii ghout its length. 'Thehecorid pole face of the 'field piece is aligned with one end of the armature and is also "spaced from it. The} armature is yield'ably t restrainedi'n areferenojepositiO I by a suppp-rtingjj fiexible many. di ion substantially in a plane perpe i tojth e cylindricalpole face. When the field piece c eratesin anyid'rectiongin the plane of orfin a plane pai'allel flexible. support in a direction opposite to thatfof the acceleration. ,This deflection of .thejarmatine, relative to the annular pole piece will upsetithe formerly uniform width of the gap about the annulus to change the reluctance of the magnetic circuit ."Disposed in the annular gap between the armature and the surrounding pole face is a coil oriented in a plane which iother engbodiinent of my invention; and

These and other objects and features of my inventioh willt-be better understood and appreciated from the fol.-

lowing detailed description of two embodiments thereof, selected .for purposes of illustration and shown in the ac FIGURE 1 is a cross sectional elevation View ofnthe preferred embodiment of an accelerometer constructed in accordancewith my invention;

FIGURE 2 is a plan view of a portion of the accelerom- Y eter shown in FIGURE 1;

FIGURE 3 is curve suggesting the output. signalof theaccelerometer shown in FIGURE 1 FIGURES 4 and 5 are diaghammatic views er the device inEIGUR'ES l and 2 illustrating the effect of displacem t of the armdtureupon the fl-uxdensity in the 7 it 6 is cross-sectionalj'elevation view. of an t ;The,"accelerometer j Silown the drawing includes in its general organization a :Ina'gnetic circuit lid-composed of ca field piece 12 and an armature, 14, and a measuring J systemlo which includes a coil 13 and an electromechanh includes the axis of the armature and field piece. The

field piece may eitherbe a iperm anent magnet or an electro'mag'net and will. provide asource of magnetic flux which flll'st'thel-annular gap. A motor is provided to rotate the coil'aboutthe axis of the armature causing the coil to cut-the lines of flux radiatingtbetween the armature-and the magnetic field piece. .I Wheirthe ap width is constant throughout theannulus, no signal'i's induced in the coil as it rotates but when the armature displaces to upset the uniformity of the gap width,a signal is induced 1 the cell, which is. sinusoidal in .nature with oneccycle for each complete c'oi laevolution. The amplitude of the signal isa measure of the maximum flux density which in turn is a measure of the displacement of the armature from the reference position wherein the gap is uniform. As the displacement of the armature is a tunecal indicating device 23.

The field piecel l of the magnetic circuit 19 may either be a perrn anent .orelectromagnet, is generally E-shapcd in crosssection as shown FIGURE 1, and includesa pole face ZZyvhichfsrirrourids the arfnature 14. Thegap between the cylindrical surface'of the armature l4 and tion of the acceleration, it will be appreciated that the amplitude of the signal is la measure of the acceleration.

To determine the direction of acceleration, numerous means may be provided to establish a. reference position for the coil. By providing a reference signal each time the pole face .22 is uniformin width asis shown clearly fee 26 aligned axially with the armature 14 and spaced below the bottom end of the armature. I

fiexi'b-lereed 2t securedto the pole face 26 extends upwardly an d supports the armature 14 -in'a reference positioriwherein its axis is concentric with the pole face 221. Thus, thegap 24 base constant width W and describes an annulus between the armature and pole face 22. Be? cause thereed 28 isiflexible, the armature 14 has complete freedom of movement about 360 in a plane substantially perpendicular tothe pole face 22 and the armain FIGURE 2-. The field piece. 12 includes a second'poie .tnreaxis. Thus, if the fieldpiece 12 is accelerated in ."thedirection of arrow A (see FlGURE 2), the armature 14 will deflect in the direction of arrow B. toward the pole face 22; Similarly, acceleration of the field piece 12 in the direction of arrow C will cause the armature 14 to deflect in the direction of arrow D, and acceleration in the direction B will cause the armature todeflect in the 3,llll,0li3 Patented Aug. 20, 1963 the embodiment illustrated,- the motor 34 carries .a plate'58 on the upper end of its upwardly extending shaft- 60 and the plate '18. :The plate 58 carries a reflector 62 at one point on direct-ion of arrow F. In each example it will be noted that the displacement of the armature is in the direction opposite to that of the acceleration to which the field piece is subjected. I p I When the armature 14is in the reference position into which itis biased by the reed 28, the flux density about the gap 24 isuniform, assuggested in FIGURE 4, wherein theflux lines areshown to be uniformlyspaced and radiating outwardly fromthearmature in the direction of pole face 22. However, when the armature 14 dis- 7 places towards oneportionof the pole. face 22, the fiux' density about the annular gap 24 is no longer uniform. 'Attention is directed" to FIGURE wherein the flux density suggested .by'the arrows in the gap 24 are most closely spaced at the location of arrow '3 representing the direction in which the armature 14 displaced within the cylindrical pole face 22 in response'to acceleration of the field piece 12 in thfidllfiCtlOjIlOf arrow A.

I ;Referring again to FIGURES I and 2, the reader will note that the coil 18 forming part of the measuring systern 16 is o'rientedi'n :a vertical plane which includes the axis'of the armature 14 and the pole face 22. I The coil 18 extends about the armature 14 and is provided with an opening 30 so as to avoid contactvwith the reed 28 The 'coil which may be made up. of several turns of electrical 7 conducting material is supported on the shaft 32 of motor 34. The motor rotates the coil 18 about the axis of the armature 14 so that the vertical legs 36 and'33 of the coil cut the lines of flux which extend across the gap 24 between the armature and pole face 22. It Will be recognized thatwhen the flux density in the gap 24 is constant as in the case sh'own'in FIGURE '4, rotation of the coil 18 in the gap will not induce acurrent in the coil. How'- 7 II ever, when the armature displaces as suggested in FIG- URE. 5 to produce a non-uniform flux density in the gap acceleration is measured bysensing the changes in re-.

24, a signal will be induced in the coil 18, sinusoidal in nature, as suggested in FIGURE 3: The curve 40 which representsthe signal induced in the coil 18 will have a maximum amplitude as indicated at 42 when one of the v legs 2:6v or 38 of the, coil passes through the point of max I, ,fiuxfdensity adjacent arrow .B. The maximum negative; amplitude 44 0f the signal 40 will occurwhen I the other of the legs 36--and 3$I.pass. through thatpoint of maximum flux density.- The signal induced inthe coil 1 will have a ze'ro value 46 whe'n'the density of the flux cut by the twoilcgs of the coil is equal. Thus, when the coil lies in aplane normal to the arrows A' and B, .the signal is I f of 'gero'v alue. "Because the flux density at any. point in the gap 24 is proportional to the width of the gap between the armature l4 and the pole face 22atth'atpoint, and

j further because the width of the gap 'is proportional to the accelerationto which the field piece 12 is subjected,'

V I the amplitude of the signal induced in'the coil is propor tional toand, thus, isJ-a measure of that, acceleration. I

The amplitude of the signal induced in the coil 18 may be measured in anyone of, several ways. -In FIGURE 1,'

I I have suggested that the signal induced in the coil 18 Y -may be fed by means ofthe slip ring assembly 50 and conductors 52 through amplifier 54 to oscilloscope 56. By means of the scope 56, the amplitude .of the signal may .bemeasured.

i i I f'The'measur'inglsl/stem is cgmpletd. by the means as vided to determine the direction of the acceleration. H In flat 58 rotates in synchronism with the :coil

its periphery. The locationof tthe reflector 62 serves to establish areference position for the coil 18. In FIG URE .1, the reflector is, positioned. to reflect the light emanating from the light source 64 to the photocell 66. Thesignal generated by the photocell is conveyed by 'leads 68 to the amplifier 54 and that signal may be supermposed on the signal induced in the coil 18 as a pulse of pip 70 as suggested in FIGURE 3. Thus, by measuraccomplish the same purpose. For example," once each revolution, the coil 18 could be shorted out across the I 'slip tin assembly 50 which wouldlproduceasin'gle pip on each cycle of the curve 40. This method would estab lish a reference position for thec'o'il'and' by measuring the time 1 between the pip created byth'e' short and'the null position on the curve thedirection ofacceleration maybe determined. ;'While I have also suggested that thesi'g nal may be measured by means of'a' scope 56, it will be appreciated that the amplitude of the signal may be measured in other ways by conventional equipment.

While in the preferredembodiment of my invention the luctance of the. magnetic circuit in the embodiment of FIGURES 6 and .7 this measurment is made-by sensing the change in capacitance in an electrical circuit 'In FIGURE'6, a cylindrical bobbin made of a non-conductive material such as ceramic. is yieldably supported in a reference position above'a support 82 by a flexible reed 84. The bobbin has a metallic skin 86 about its side wall and is surrounded by a second cylinder 88 also made of a non-conductive material. The cylinder 88 is carried on the shaft 90 of motor 92 and is caused to rotate by that motor about anaxis coincident with the bobbi axisin the reference position illustrated.

A U-shap'edelectrode 94 may be painted with a con ductive material or similarly' secured to the inner surface of the cylinder 88 so as to provide a pair of arms 96 and.

98 displaced 180 apart and spaced equal distances from the skin 86 of thebobbinf80. The electrode 94 and the 7 skin 86 form theplatesof a capacitor and are separated by an air'gap'whichfisuniform as the cylinder 88-rotates,

. so) long as the bobbin remains in lthe xreference position. 'lhecapacito'r formed by the electrode 94- andfthe skin 86 isconflectedjacross a battery "1G0 andin series with resistorfliiz by means of leads '104'and 106 and'slip ring assembly 108. If the resistor 102 has a large value, the "voltage across thecapacitorwill be:proportionaltothe i gap width between the plates, 'i.e.' between the skin" and .1 the electrodev arms 9 6and 98. :As' long as the bobbin re mains in itsreferenceiposition, the capacitance remains the same 'and the voltage across" the capacitor remain's constant. However, when'thebobbin displacesin response to acceleration of the instrument, thegap width between the skin 86 and the, electrodes will vary as the cylinder 88-rotates about its axis; Thus, the signal-across the capacitor will be sinusoidal in nature, taking the form of ourve40'in FIGURES. This signal may be amplified I and directed tothe scope 56gby means, of leads 110 and 1-12, slip ring assembly11tl8 and amplifier 54. 'As the width'oftheygap is proportional to theacceleration of the instrument and the amplitude ofthe signal is propertion al to the gap width at its smallest point, the amplitude I of the signal is proportional to the acceleration. a

The. direction of displacement of the bobbin may be determined in any one of several ways. '1 For example, the

electromechanical means disclosedin FIGURE 1. could be added to the structure of FIGURE 6 and accomplish the same function. Alternatively, once each revolution .of the cylinder 88 the plates of the capacitor could be instantaneously shorted to establish a reference position for the cylinder 88 and impose a pulse on the sinusoidal signal. By measuring the time between the'pulse and the point of maximum amplitude of the curve on the scope,

the direction of acceleration may be determined.

Because numerous modifications may be made of my invention as suggested above without departing from its their equivalents.

. by movement of the armature.

V spirit, it is not my intention to limitthe breadth of my invention to the specific embodiments illustrated and described. Rather, it is my intention that the breadth of my invention be determined'by the appended claims and What I claim as new and desire to secure by Letters Patent of the United States is:

l. A polar. accelerometer comprising a magnetic field piece having an annular fir'stpole piece and a second pole piece disposed on the axis of the first pole piece, a cylindrical "armature surrounded by the first pole piece and defining with the field piece a magnetic circuit, the diameter of the armature being smaller than the inner diameter ofthe annular pole piece to form an annular gap in said circuit, a flexible reed yieldably supporting said armature 'coaxially with the pole piece and providing said armature with freedom of movement substantially in the plane of the pole piece to vary the radial width of the gap about the annulus, said armature moving in said plane in response to acceleration of the field piece, a coil disposed inthe plane of the axis of the poles and in part disposed in the gap, means for rotating the coil about said axis causing the flux in the gap to induce an alternating signal in the coil when the density in the gap is non-uniform,

means for measuring the amplitude of the signal, and means for imposing on said signal a second signal establishing a reference position for said coil during each revolution.

2. A polar accelerometer comprising a cylindrical armature, a magnetic field piece including an annular pole piece surrounding and spaced from the armature, a second pole piece forming part of the field piece and spaced from one end of the armature, said field piece and armature together forming a magnetic circuit with a uniform flux density in the gap between the armature and annular pole piece, means supporting said armaturein said circuit and enabling said armature to move in the plane of the first pole piece to vary the flux density about the gap, a coil rotatably mounted in the gap for rotation about the axis of the annular pole piece, said coil carrying an induced alternating signal Whose amplitude is proportional to the displacement of the armature. in the gap, and means for measuring the amplitude of the signal. j e

3. In a polar accelerometer, a magnetic circuit having an armature, surrounding magnetic field "piece, and-an annular, gap between thearrnature and field piece; 'rneans',

enabling said armature to displace in response to accelera- 6 signal which is a function of the variations in gap width, and means for measuring the magnitude of the signal.

6. In an accelerometer, a magnetic circuit including a circular armature and surrounding annular pole piece spaced from thearmature and defining a gap between them, means yieldably supporting the armature in a reference position wherein said gapwidth is uniform, said means enabling said armature to displace radially relative to, said pole piece in responseto acceleration of the armature to vary the gap width, said radial movement being in a direction opposite to the direction of acceleration of the armature, a conductor movable in the annular gap about the axis of the piece and establishing a signal which is a function of the width of the gap, and means for.

measuring said signal. V

7. A polar accelerometer comprising a magnetic circuit including an armature and an adjacent pole piece spaced tion of said accelerometer radially within the field piece in a direction opposite to the direction of acceleration to vary the flux density in the gap, a conductor disposed in, the gap, means moving said conductor about the annular. gap causing it to cut the lines of fluxestablished in the gap, andmeans for 'measuring the signal induced insaid conductor by the variations in flux densityin the gap effected 4. A polar accelerometer comprising, a magnetic circuit including an armature and an adjacent pole piece spaced apart to define a gap having a uniform ilnx density, a

flexible support for the armature enabling said armature to move in response to acceleration of the accelerometer apart to define a gap having a uniform flux density, means yieldably supporting said armature enabling said armature to move in response to its accelerationtoward the pole piece to increase the flux density in the gap at a location indicative of the direction of the acceleration, and means including a conductor cyclically movable through the gap and cutting the lines of flux in the gap for establishing a signal whose maximum amplitude is a function of the flux density at said location, and means for establishing a reference position for the conductor in the gap as it moves through each cycle.

8. Acceleration sensitve apparatus comprising, an element supported on a body -whose acceleration is to be sensed, said element being normally oriented relative to said body in a reference position when the velocity of said body is constant, means for supporting said element to prevent relative movement between said element and said body along a first line of direction while allowing relative movement in the plane orthogonal to said first line of direction, means including said element for establishing a field external to said element, field sensitive means relatively movable with respect to said element and responsive to relative periodic motion betweensaid position, and means responsive to said field sensitive means and said element assuming a predetermined refference relative position for providing a periodic reference signal, the time displacement between said reference signal and said periodic signal being characteristic the direction of said acceleration.

9. Acceleration sensitive apparatus in accordance with claim 8 and further comprising, means for comparing said reference signal with said periodic signal to derive an indication of said acceleration direction, and means responsive to the amplitude of said periodic electrical signal from said field sensitive means for providing an indication of the magnitude of said acceleration.

toward the pole piece at a location indicative of the direc tion of the acceleration to establish a non-uniform flux: density in the gap, and means including a conductor mov ing through the gap and cutting the lines of flux in the gap and establishing a signal whose value is a'function of the flux density at each point in the gap. i

5. In a polar accelerometer, a-magnetic circuit including an armature and a pole piece defining a gap'of constant width throughout its length, a flexible supportfor '10. In apolar accelerometer, fieldestablishing means including anarmature -and, another member defining. a gap of predetermined width throughout its length, a

flexible support for, the armature enabling, said armature to movein response to acceleration ofthe accelerometer toward saidanother member to effect variation in the -wic lth along the length of the. gap, said flexible support returning said armature to a predetermined reference position in the absence of acceleration, means responsive to the field established in said gap for'providin'g a signal 'which is a function of said variations in gap width, and

means for measuring the magnitude of the latter signal.

the armature enabling said armature to move in response tions in the Width along the length of the gap, a conductor moving through the length of said gap and establishing a to its acceleration toward the pole piece at a location in- 7 l1..Apparatus in accordance with claim-1Q wherein said armature and said another member define an annular gap of substantially constant width throughout its circumferential length when said armature resides ,in

said reference position, and means for supporting said armature relative to said another member to prevent relativemovement between said armature and said an- 2,613,071 Hansel V Oct 7, 1952 I 7 7 other member, in a direction generally parallel to the axis of said annularlgap while allowing relative movement therebetween in :a'plane orthogonal to said'axis.

References Cited in the file of this patent UNITED STATES PATENTS Carlstein Aug. .7, 1945 Great Britain 

10. IN A POLAR ACCELEROMETER, FIELD ESTABLISHING MEANS INCLUDING AN ARMATURE AND ANOTHER MEMBER DEFINING A GAP OF PREDETERMINED WIDTH THROUGHOUT ITS LENGTH, A FLEXIBLE SUPPORT FOR THE ARMATURE ENABLING SAID ARMATURE TO MOVE IN RESPONSE TO ACCELERATION OF THE ACCELEROMETER TOWARD SAID ANOTHER MEMBER TO EFFECT VARIATION IN THE WIDTH ALONG THE LENGTH OF THE GAP, SAID FLEXIBLE SUPPORT RETURNING SAID ARMATURE TO A PREDETERMINED REFERENCE POSITION IN THE ABSENCE OF ACCELERATION, MEANS RESPONSIVE TO THE FIELD ESTABLISHED IN SAID GAP FOR PROVIDING A SIGNAL WHICH IS A FUNCTION OF SAID VARIATIONS IN GAP WIDTH, AND MEANS FOR MEASURING THE MAGNITUDE OF THE LATTER SIGNAL. 